1. Field of the Invention
The present invention relates to well packers that are hydraulically set or anchored at a downhole location within a well bore by fluid pressure acting upon one or more pistons. Fluid pressure on the piston(s) generates sufficient force to compress packing elements which establish a fluid barrier and to radially expand slips which anchor the packer at the desired downhole location.
2. Description of the Prior Art
Hydraulically set well packers have been used in the oil and gas industry for many years. Examples of such prior packers are shown in U.S. Pat. No. 3,112,796 to W. D. Meyers; U.S. Pat. No. 3,136,364 to W. D. Meyers; U.S. Pat. No. 3,189,095 to J. F. De Rochemont; and U.S. Pat. No. 3,221,818 to F. H. Taylor et al. These patents are incorporated by reference for all purposes within this application.
Hydraulically set well packers are generally installed within the bore of a casing string which was previously cemented in place to define the well bore. Such packers are attached to a production tubing string at the well surface and lowered to the desired downhole location within the bore of the casing string. During this time period, the casing string is generally filled with a fluid such as drilling mud, salt water, or completion fluid. Movement of the tubing string and attached well packer into the casing bore causes the fluid to be displaced therefrom. This fluid displacement in turn tends to generate a difference in fluid pressure across the setting piston which may prematurely set the well packer before it reaches the desired downhole location. U.S. Pat. Nos. 3,112,796; 3,136,364; and 3,221,818 disclose various sliding sleeves which isolate the setting piston from fluid pressure until the respective packer is at its desired downhole location. In each patent, a ball is used to shift a sleeve from its first position blocking fluid pressure to its second position which allows fluid communication with the associated piston to set each well packer.
As shown in the prior art patents, shear pins, snap rings, and other devices are frequently used to releasably engage various components of each well packer to its mandrel. These devices prevent undesired movement of the components which could result in setting of the packer before it reaches the desired downhole location. These prior art devices, especially shear pins, are sometimes accidentally released or sheared by contact between the well packer and the inner wall of the casing string.